1. Field of the Invention
The invention disclosed and claimed herein is in the field of energy conversion. More particularly, the disclosed invention relates to an engine construction conceived for the purpose of converting heat energy into mechanical motion.
2. Description of the Prior Art
The most relevant prior art with respect to the disclosed invention is believed to be U.S. Pat. No. 4,086,769 (Smith), found with art in Class 60, Subclass 527 in the U.S. Patent and Trademark Office. The engine disclosed in the Smith patent comprises a plurality of spring-like elements made of shape-memory material, each of which is secured within a chamber and operatively connected with a plunger rod, a wrist bearing, a connecting rod, and a crankshaft and coordinated with similar spring-like elememts to drive the crankshaft. Shape-memory materials, for example, a nickel-titanium alloy, known as Nitinol, are materials which may be easily deformed with little force at a relatively low temperature and which upon being heated to a relatively high temperature will quickly, automatically revert with great force to an original shape in a physical phenomenon commonly referred to as shape-memory effect. Such material acquires its shape-memory or original shape after being subjected to a heat treatment or annealing process. After a shape-memory has been acquired by such material, it may thereafter be alternately cooled below and heated above a critical temperature to be respectively easily deformed from and allowed to revert with great force to its memory shape. Operation of the Smith apparatus is achieved by alternately heating and cooling the shape-memory elements by introducing hot and cold fluids into the chambers of the various shape-memory elements.
In accordance with the prior art then, apparatuses utilizing the power of a shape-memory alloy to perform useful work including means capable of providing periodic temperature variation necessary to the operation thereof are known. Control means may be provided to effect output power or speed by use of shape-memory elements. As it is known that shape-memory elements, when heat treated to a particular memory shape, can thereafter be mechanically deformed, when cold, by much less force than they exert upon being heated and spontaneously returning to their memory shape, the difference in force exerted may be applied to a crankshaft of perform useful work. While it is known in the prior art to use nickel-titanium alloys known as Nitinol to form shape-memory elements, other more workable alloys may later become used for the same purpose. Since the development of Nitinol, it has been recognized that when this alloy of nickel and titanium has been heat treated to a particular shape, it will acquire a memory shape which can be mechanically deformed at a low temperature to a limit of about 8% outer fiber strain and then return to its memory shape upon being heated in accordance with a Martensitic transformation. When this alloy is below its transformation temperature, the force needed to deform it is small. Once heated above its transformation temperature, it attempts to return to its memory position with great force. It is also known that the transformation temperature of Nitinol can be varied from -90.degree. F. to +275.degree. F. or more, by changing its composition. Some engines have already been made using Nitinol to convert heat energy into mechanical energy. Such engines, however, depend on an external source of heat and cold fluids for operation. Moreover, the circulation of fluid around the shape-memory elements in such engines slows down the RPM.
It is also known that the TTR range of the Nitinol elements used in such an engine widens greatly under a load (NASA SP-5110).